Confinement method and device in particular for a special atmosphere in a space for continuously processing articles fed therethrough

ABSTRACT

The present invention relates to a method for confining an atmosphere (B) in a space (4) communicating with its surroundings via at least one opening. A gas curtain (1+2) comprising a low-velocity jet (2) and a high-velocity jet (1) is generated at said opening. Characteristically, a fraction of the flow in said low-velocity jet (2) is injected into the confined atmosphere (B) and adds to the induced flowrate of said low-velocity jet (2), the size of said fraction being variable depending on the pressure within said space (4). The present invention also relates to a device for carrying out said method.

The present invention has for its object a method and a device forconfinement of an atmosphere in a space communicating with the outsidethanks to at least one opening; a gas curtain being generated at thelevel of said opening.

This method and device are advantageously employed for the confinementof a special atmosphere in a space for continuously processing objectsor articles fed therethrough. According to the prior art, to Applicants'knowledge, particularly when such processing employs explosive, toxicand/or contaminating substances, they are employed discontinuously.Thus, when it is desired to process articles in an atmosphere presentingparticular characteristics which must be maintained between precisevalues (characteristics of temperature, hygrometry, gaseous composition,concentration of liquid or solid particles in suspension . . . ), onegenerally proceeds in spaces provided at the entrance and at the exitwith chambers with tight double doors. Under such conditions:

processing can be effected only by successive batches;

the quantity of articles processed depends on the volume of thechambers;

the successive filling and emptying of the chambers bring about a lossof matter and energy, proportional to the volume of said chambers . . .

According to the present invention, an improvement to the conventionaltechnology of the confinement of a space by a double-jet gas curtain isproposed more precisely. Said technology is illustrated in particular inPatent Applications FR-A-2 530 163 (confinement of a polluted space) andFR-A-2 652 520 (confinement of a "clean" space). According to the saidtechnology, the double-jet gas curtains are used for separating twospaces containing atmospheres of different characteristics. Such gascurtains are intended to stop any solid or liquid particles insuspension in the atmospheres of the separated spaces but must, however,allow the passage of macroscopic objects passing therethrough withoutexchange between said separate atmospheres.

Such gas curtains comprise a slow jet of which the point (the innercone: potential flowing zone) ensures the dynamic separation of theatmospheres and a fast jet which stabilizes and rigidifies said slowjet.

Incidentally, it is recalled here that the flow of a jet of gas, in anysection thereof, is generally the sum of the initial flow of gas blownin and of the flow taken by suction in the gaseous environment outsidethe jet. This second flow constitutes the induced flowrate of said jet.

Opposite the jet emission nozzles, there is generally found a suctionorifice which collects the gas blown as well as a fraction of theseparate atmospheres which are mixed with said blown gas in theinduction zone. The gases collected by such a suction orifice aregenerally processed before recycling or rejection in the environment.The matter and energy lost by the suction flow are considered asnecessary and/or negligible vis-a-vis the result sought. However, thesuction orifice does not systematically take up the double jet. Thenozzles for emission of the fast jet and of the slow jet are suppliedwith non-polluted gas. They generally present a slight inclination,towards the outside of the opening of the space to be confined, suchthat in the hypothesis of confinement of a "clean" zone to be protectedfrom the outside pollution (context of document FR-A-2 652 520)--thatface of the fast jet located towards the space to be confined isvirtually parallel to the plane of said opening. Said "clean" space tobe confined is supplied by a flow of non-polluted gas, called clean gasstream, slightly greater than the flowrate induced by the inner face ofsaid fast jet (located towards the space to be confined); the excessflowrate with respect to the latter ensuring a slight leakage rate whichprevents the penetration of the fast jet in said space to be confined.In any case, according to the prior art, the nozzles of the gas curtainnever inject gas directly in the space to be confined.

Conventionally, when it is question of protecting an environment from"pollution" (the "pollution" being located inside or outside the spaceto be confined), the fast jet is always located towards thenon-"polluted" side.

The double-jet gas curtain is generally a curtain of air. The airinjected in the form of slow and fast jets is returned into circulationor rejected, after filtration of the particles in suspension entrainedin the suction orifice.

According to its first object, the invention therefore relates to amethod for maintaining a particular atmosphere in a space communicatingwith the outside thanks to at least one opening protected by adouble-jet gas curtain. Said atmosphere is special in that it isdistinguished from the ambient atmosphere by at least onedifferentiating element which, for example, may consist of aconcentration of particles, a concentration of gas, a temperature, . . .Said special atmosphere or differentiated atmosphere is thereforeconfined in said space. According to the context, said specialatmosphere is a clean atmosphere or a polluted atmosphere with respectto the ambient atmosphere. The slow jet of the gas curtain is disposedtowards said confined atmosphere in order to avoid the turbulenttransfers due to the passages of the objects passing therethrough. Theaxial plane of the emission nozzle of the slow jet and that of theemission nozzle of the fast jet are parallel. Said nozzles may bedisposed on any one of the sides of the opening.

More precisely, the method of the invention is a method for confinementof an atmosphere in a space communicating with the outside thanks to atleast one opening; method in which:

a) a curtain of gas is generated at the level of said opening; said gascurtain comprising:

a first jet, called slow jet, located towards said confined atmosphere;said slow jet presenting a point of range (L) and spread sufficient tocover said opening;

a second jet, called fast jet, located towards the outside, in the samedirection as said slow jet, of which the axial plane is parallel to thatof said slow jet; said fast jet having a flowrate induced by its innerface in contact with the slow jet less than or equal to the flowrate ofsaid slow jet at a distance (L), equal to the range of said slow jet,from its injection;

b) at least a part of the gas blown in in the form of said slow and fastjets as well as a fraction of the confined atmosphere are taken up, atthe level of said opening, opposite the injection zone of said jets;

c) a supply of said space with adequate atmosphere is advantageouslyprovided, in order at least to compensate said fraction of the confinedatmosphere taken up;

d) a fraction of the flow of the slow jet is injected in said confinedatmosphere and contributes to the induced flowrate of said slow jet; thesize of said fraction varying with the pressure within said space.

According to the method of the invention, a double-jet gas curtain istherefore employed, the slow jet of said curtain being located towardsthe special confined atmosphere (point a) hereinabove) and, opposite theinjection zone of the jets, a device, including a suction orifice fortaking up the gas blown in in the form of said jets and a fraction ofsaid confined atmosphere (point b) hereinabove). A fraction of theambient atmosphere is also generally taken up, at the level of saidsuction orifice. Said jets and said suction orifice are disposed so asto maintain in the confined atmosphere characteristics which areconstant or included between precise values. As will be explainedhereinafter, their particular arrangement makes it possible to minimizethe losses of matter and/or energy by the take-up flowrate andconsequently to minimize the continuous additions necessary formaintaining said particular characteristics of the confined atmosphere.In fact, insofar as it is desired to ensure such maintenance, anadequate supply of said space is provided, at least to compensate thefraction of the confined atmosphere taken up point c) hereinabove) andadvantageously to contribute to maintaining the confined space in slightoverpressure. Said space is thus efficiently protected from the ambientatmosphere.

However, the man skilled in the art will understand that the method ofthe invention may also be carried out without such a supply point c)hereinabove), insofar as the take-up of the confined atmosphere is,according to the invention, minimized and in any case is compensated byblown in gas taken from the zone of induction of the slow jet. However,such conditions of implementation (without supply) which are notexcluded from the scope of the present invention, do not ensure anoptimum result. Under these conditions, the confined atmosphere willlose its characteristics of differentiation after a more or less longperiod. This may be considerably detrimental in the context of acontinuous processing of traversing products by a reagent present insaid confined atmosphere . . . It is much less so, for example, in acontext where it is desired simply to maintain said confined atmosphereat a given temperature and where the slow jet supplies gas at saidtemperature . . . As indicated hereinabove, according to an advantageousvariant of the method of the invention, a supply of adequate atmosphereof the confined space is therefore provided.

Finally, and here it is question of the principal characteristic of themethod of the invention, a fraction of the flow of the slow jet is sentinto said confined atmosphere (point d) hereinabove). Said fraction istaken in the induction zone of the slow jet, on the confined space side,of course. It is not directly taken up by the suction orifice. Itpenetrates in said confined atmosphere, generates turbulences thereinand is at least partly taken up by the slow jet for induction thereof.In this way, the induced flowrate of the slow jet is, characteristicallyaccording to the invention, taken partly on itself (towards the confinedspace). Towards the confined space, said slow jet is self-stabilized. Infact, a part of it is "recycled" in the confined space to that end. Onthe ambient atmosphere side, it is recalled here that said slow jet isstabilized by the fast jet.

This gas injected in the confined atmosphere, taken on the slow jet, isused:

for homogenizing said confined atmosphere,

for creating a certain overpressure within it,

for regularizing the take-up of said injected gas and said confinedatmosphere.

The method of confinement with double-jet gas curtain is in fact carriedout according to the invention under conditions such that an effect ofregularization of the extracted flow of confined atmosphere is observed,with maintenance of homogeneous conditions in said confined atmosphere.This effect of regularization is particularly interesting when the gascurtain defines a processing chamber in which a specific reagent must bemaintained in sufficient concentration in the atmosphere for theduration of the processing. In fact, the incurvation of the curtainprovoked by the overpressure (due pricipally to the injection in theconfined space of a fraction of the flow of the slow jet) allows escapeonly of a weakly concentrated fraction of said specific reagent of themixture between the gas blown by the slow jet and the processingatmosphere (said processing atmosphere having been diluted by theaddition of "pure" gas of the slow jet) and therefore brings about onlya negligible consumption of said reagent. Moreover, as indicatedhereinabove, the turbulence generated inside the processing chamber (byinjection of a fraction of the flow of the slow jet within it)homogenizes the distribution of said reagent in the atmosphere of thechamber, reagent advantageously continuously added in said chamber tocompensate the losses.

Furthermore, it will be insisted upon, according to the method of theinvention, that the gas curtain is not stiff, stabilized in a fixedposition. Under the effect of a variation in pressure within theconfined atmosphere (which pressure variation may be due to a variationin the adequate atmosphere supply flowrate and/or to the arrival of anobject of large volume in the confined space), the jets move and a moreor less large fraction of the flow of the slow jet is sent into theconfined atmosphere.

According to the invention, the technology of the double-jet gas curtainhas been adapted so as to minimize the losses of matter and/or energycoming from the confined atmosphere, via the suction orifice, whilehomogenizing the characteristics of said confined atmosphere.

The man skilled in the art will already have understood that theprinciple of the method of confinement according to the invention, asset forth hereinabove--with injection of a fraction of the flow of theslow jet in the confined atmosphere, which allows a regulation of theflow of said sucked confined atmosphere (while, according to the priorart, no regulation is observed of said flow of confined atmosphereextracted)--may be carried out in accordance with differentconfigurations, and this in different contexts, particularly at theentrance and/or exit of painting tunnels, sterilization tunnels,processing ovens, drying ovens, . . .

A thermal confinement of the space may simply be sought, the othercharacteristics of the separate atmospheres being identical. The gascurtain will in this context be generated from the same atmosphere withat least one thermostated slow jet which will maintain the temperaturein the confined space. By way of example, the production of cold or hottunnels on object-conveying elements may be cited. The method of theinvention makes it possible, in this context, for the objects tocirculate continuously, limiting the losses of energy and thetemperature gradients at the level of the inlets and exits of saidtunnels.

The method of the invention may also be employed for packing possiblytoxic and/or dangerous pulverulent products, and for the advantageouslycontinuous processing of different types of products. By way of exampleof such processing, the smoking of agri-food products or thesterilization of objects by spraying liquid and/or gaseous disinfectantsin the pharmaceutical industries may be cited.

Particular emphasis will be made on the advantage of carrying out themethod of the invention for the confinement of a space for continuouslyprocessing products or objects passing therethrough, advantageouslyintegrated in a line for conveying said products or objects. Such aprocessing space comprises a gas curtain at the inlet and a gas curtainat the exit; gas curtains which are generally flat, through which theobjects or products to be processed, transported by the coveyor system,successively pass. If the spaces upstream and downstream of theprocessing space are at the same pressure, the two gas curtains functionsymmetrically and the same effect of regulation of the suction flowrateof confined atmosphere is obtained on said two curtains.

The method of the invention may be implemented in accordance withdifferent variants. Advantageously, the expected result is obtained witha plane of the gas curtain which is inclined with respect to the planeof the opening, towards the interior of the confined space. Said gascurtain plane makes an angle with said opening plane, with the resultthat the end of the point of the slow jet is oriented towards theinterior of the confined space. Said angle of inclination of the medianplanes of the gas jets with respect to the plane of the openinggenerally remains less than or equal to 30°. For certain applications,it advantageously makes it possible to increase the pressure in theconfined space with respect to the outside pressure. Such increase inpressure (which generally remains of the order of a pascal) is due tothe transformation of the dynamic pressure of the recycled fraction ofgas into static pressure. It is a function of the value of said angle ofinclination and of the shape of the suction orifice.

The or each gas curtain employed in the method of the invention maypresent varied geometries. It may be question of gas curtains generatedby linear, polygonal or arcuate nozzles. The plane of the gas curtainwill consequently describe, possibly with the above-mentionedinclination, either a plane or a portion of polyhedron, or a truncatedsurface portion. The geometry of the gas curtain is obviously adapted tothat of the opening to be covered or to that of the confined space.

The gas curtain constituted by the two jets is generally generated fromnozzles which may be located on a horizontal or vertical side of theopening giving access to the confined space.

Furthermore, as indicated hereinabove, according to a variant of theinvention, at least one of the jets of said gas curtain, generally theslow jet (and advantageously the slow jet and the fast jet) is suppliedwith thermostatted gas. The gas supplying said slow and fast jets maygenerally present the same characteristics (for example: nature of saidgases, temperature thereof, . . . ) or different characteristics.

Finally, it is specified that the gas curtain (or gas curtains) asemployed in the method of the invention--gas curtain(s) with regulationof take-up flowrate--generally consist(s) of a curtain with double airjet. However, for certain applications, it is not excluded that the airbe replaced by any other appropriate gas, particularly an inert gas inone jet only or the two jets. Neither, as indicated hereinabove, is itexcluded that the injected gases, of the same nature or of differentnature, may present different characteristics, particularly oftemperature, hygrometry, concentration of liquid or solid particles insuspension.

In accordance with its second object, the invention relates to a deviceuseful for carrying out the method described hereinabove. Said devicecomprises the conventional means necessary for generating and operatinga double-jet gas curtain at the level of an opening. In characteristicmanner, within said device, said means are arranged to ensure theexpected effect described hereinabove, i.e. the injection of a fractionof the flowrate of the slow jet, for auto-induction thereof, in theconfined space.

More precisely, said device comprises:

two nozzles disposed side by side on one side of said opening andprovided with means for supplying gas thereto; the length of saidnozzles being at least equal to the length of said opening, the width ofsaid nozzles being determined as a function of the velocity of the jetsand the range of the curtain to be obtained; the nozzle located towardsthe confined atmosphere being suitable for the emission of the slow jetand the other for the emission of the fast jet;

an orifice for suction of at least a part of the gas blown in in theform of jets and of a fraction of the confined atmosphere, said suctionorifice being connected to a suction system and being located at thelevel of said opening, opposite said two nozzles;

advantageously a system for supplying the confined space with adequateatmosphere.

Characteristically, said gas suction orifice is positioned with respectto said two nozzles so that, and presents a geometry such that afraction of the flow of the slow jet is injected in said confinedatmosphere and contributes to the induced flowrate of said slow jet; thesize of said fraction varying with the pressure within said confinedspace.

It will be noted that, at the level of said suction orifice, ambientatmosphere is in general also sucked.

Within said device, the two injection nozzles are advantageouslyoriented so that the plane of the gas curtain is inclined, with respectto the plane of the opening, towards the interior of the confined space.The angle of inclination as indicated above is included between 0 and30°.

The position and geometry of the suction orifice must allow normaloperation of the gas curtain as from starting and creation of a slightoverpressure in the confined zone.

The gas suction orifice is disposed opposite, generally plumb with thegas supply of the curtain. In fact, it comprises a cavity for receivinggases which communicates with a conduit for evacuation thereof. Saidcavity is advantageously connected to at least one of the material wallswhich define the opening.

In the more general context of the vertical or substantially verticalgas curtain, supplied with gas blown from top to bottom, the gasreceiving cavity is advantageously connected to the base, to the floorof the confined zone.

In this context, the nozzles are disposed in the upper part of theopening and said cavity is located below the level of the base of theconfined zone (floor of said zone). It is advantageously defined, on theslow jet side, by an edge with concave curvilinear profile, connected tosaid base of the confined zone. Said edge does not present an edgecapable of generating turbulences. Its profile is concave, with theresult that it "accompanies" the deformation of the end of the pointunder the effect of the overpressure.

The position and geometry of said cavity must allow normal operation ofthe gas curtain, in the absence of consequent overpressure in theconfined zone. In this context of normal operation, the thinned end ofthe point of the slow jet arrives at the limit of the curvilinear edgeof the cavity. Under the effect of a consequent overpressure, said endwill deform and clear along said curvilinear edge a passage for theconfined atmosphere (atmosphere in fact diluted in gas taken from theslow jet).

The device of the invention and its functioning will be described moreprecisely with reference to the single accompanying FIGURE hereinafterin the present text.

According to a variant of said device of the invention, the confinedspace is defined by a ceiling, a floor and at least two lateral walls.There may be three lateral walls and one sole opening to be covered by agas curtain or only two parallel lateral walls and two openings to becovered by two parallel gas curtains. The injection nozzles of the gascurtain(s) are generally located at the level of the ceiling of theopening(s), the gas curtain(s) is/are substantially vertical and thesuction orifice is integrated in the floor. The cavity for reception ofthe gases associated with said suction orifice is located beneath thelevel of said floor and is defined in width by the walls of the confinedspace.

According to another variant of the device of the invention, theconfined space is defined by a circular ceiling, a circular floor and acylindrical or truncated gas curtain. In this configuration of thedevice of the invention, the cavity of the suction orifice, opposite thecircular gas injection nozzles, constitutes a pit around said base.

According to another variant of the device of the invention, theconfined space is defined by a polygonal ceiling, a polygonal floor anda polyhedral gas curtain. In this configuration of the device of theinvention, the cavity of the suction orifice, opposite the polygonal gasinjection nozzles, constitutes a pit around said base.

The method and device of the invention are illustrated in accompanyingFIG. 1.

Said FIG. 1 shows in section the confinement according to the inventionof atmosphere B in a chamber 4 for continuously processing a product P,by a reagent R injected via tube 8. The product P is conveyed by theconveying system 11. The chamber 4 is defined by a horizontal ceiling, ahorizontal floor, two vertical walls (not shown) and two plane verticalair curtains. The products P to be processed arrive from atmosphere A(ambient atmosphere, for example), pass successively through the inletair curtain and the exit air curtain and are found again in saidatmosphere A. Each of said air curtains comprises a slow jet 2, locatedtowards the chamber 4, of which the point 3 is inclined towards theinterior of said chamber 4 as well as a fast jet 1, locateds towards theoutside (atmosphere A). The system for suction of the blown-in gas and afraction of the confined atmosphere B is disposed plumb with theinjection nozzles 9 and 10. Said suction system comprises the cavity 6for receiving the gases and the conduit 7 for evacuation of said suckedgases. Said cavity 6 is defined towards the slow jet 2 by an edge 5 ofconcave curvilinear profile which joins the floor of the chamber 4.

The cavity 6 for receiving the gases has a geometry and a positioningwith respect to the nozzles 9 and 10 such that, in stationary regime andin the absence of disturbance, the point 3 of the slow jet 2 is in theposition of equilibrium, between the atmospheres A and B, shown in solidlines in FIG. 1. The flow of gas entrained by the slow jet 9 in itscross section located at the distance L from its origin is divided onthe curvilinear edge 5 of the cavity 6 constituting the orifice fortake-up of the double jet 1+2.

The major fraction of the flow of gas of the fast jet 1 and slow jet 2is sucked by the take-up orifice 6 and evacuated via conduit 7. Afraction of this flow is injected in the confined space 4, inducing astream which promotes homogenization of the atmosphere B. This"recycled" fraction is added to the light flow of reagent R introducedat 8 to ensure the induced flow rate at the interface between the slowjet 2 and the atmosphere B. The product of the average concentration inthe fraction of atmosphere B extracted by its flowrate then correspondsto the addition of reagent R in the enclosure 4 via conduit 8.

If a disturbance increases the flow of reagent R introduced at 8, theresulting increase in pressure in the enclosure 4 has for its effect toincurve both of the two jets and to displace the point 3 of the slow jet2 in the position shown in dotted lines in FIG. 1. This displacementbrings about a reduction of the fraction of the flow of the slow jet 2injected in the enclosure 4 associated with an increase in the flow ofatmosphere B extracted. Furthermore, the average concentration ofreagent R of said flow of atmosphere B extracted is all the higher asthis flow is greater.

Symmetrically, if the flowrate of reagent R incidentally decreases, thereverse phenomenon occurs. The point 3 of the slow jet 2 moves towardsthe interior of the enclosure 4. This displacement brings about anincrease in the fraction of the flow of the slow jet 2 injected in theenclosure 4 associated with a decrease in the flow of atmosphere Bextracted. In the same way, the average concentration of reagent of saidflow of atmosphere B extracted is all the lower as this flow is less. Inthe case of the flow of reagent R being entirely consumed by theprocessing of the objects P passing through, the flowrate of thefraction of the slow jet 2 injected in the enclosure 4 becomes equal tothe induced flowrate at the interface between the slow jet 2 and theatmosphere B that it compensates entirely. The method thereforeadvantageously enables the consumption of reagent to be limited.

The invention is illustrated by the following example, with reference toFIG. 1.

With the aid of two air curtains, a chamber 4 for continuouslysterilizing pharmaceutical products P is confined. Sterilization isobtained by contact of said products P with a sterilizing gas ornebulized liquid (H₂ O₂) at an optimal temperature. In order to attainand maintain said optimal temperature, two thermostatted slow jets areused. The two air curtains prevent any leakage of H₂ O₂ towards theadjacent zones (atmosphere A).

The inclination of the points 3 of the slow jets 2 towards the interiorof the chamber 4 makes it possible to entrain the contaminatingparticles which accompany the products P towards the zone of processingby sterilization (atmosphere B), at the inlet and at the exit.

The injection of a part of the air of the slow jet 2 in the chamber 4generates therein eddying movements which contribute to thehomogenization (concentration, temperature) of the sterilizing medium atthe centre of said chamber 4.

The effect of depletion of sterilizing reagent in the vicinity of thepassage of outflow limits the losses of said reagent and maintains itsconcentration at the required level for the duration of the processing,optimalizing consumption thereof.

Said method of confinement is carried out under the followingconditions:

The chamber 4 is a tunnel of section 0.5×0.5 m. An atmosphere of H₂ O₂is maintained therein at 15 g/m³.

The slow jets 2 present the following characteristics:

Initial velocity: v_(o) =0.5 m/s

Flowrate: Q_(o) =0.025 m³ /s

They are injected through nozzles 9 presenting a length of 50 cm (lengthof the opening of the tunnel) and a width (of slit) of 10 cm. The rangeof the point 3 of said slow jets 2 is 60 cm.

The fast jets 1 present the following characteristics:

Initial velocity: v_(o) =8.17 m/s

Velocity at 0.5 m: v=2 m/s

Initial flowrate: Q_(o) =0.020 m³ /s

They are injected through nozzles 10 presenting a length of 50 cm(length of the opening of the tunnel) and a width (of slit) of 5 mm.

At the level of the evacuation conduits 7, the take-up flowratecorresponds to the sum of the flowrate of the fast jet 1, of the slowjet 2, of the supply of sterilizing reagent (variable flowrate), andpossibly of the ambient atmosphere (A) sucked (variable flowrate).

We claim:
 1. A method for confinement of an atmosphere in a spacecommunicating with the outside by at least one opening by means of acurtain of gas provided at the level of said opening, said methodcomprising the steps of:providing a first gas jet, forming a slow jet,having a first side facing said space and a second side, an injectionend, a dart of a range L and a spread adapted to cover the entiresurface of said opening; providing a second gas jet, forming a fast jet,having a first side facing the outside, a second side facing said secondside of said slow jet, and an injection end, said fast jet having thesame direction as said slow jet and an axial plane parallel to that ofsaid slow jet, said fast jet having a flowrate induced by its secondside in contact with said slow jet not greater than the flowrate of saidslow jet at a distance L corresponding to the range of said slow jetfrom its injection end; said slow and fast jets constituting saidcurtain of gas; causing at least a part of the gas blown in the form ofsaid slow and fast jets as well as a fraction of the confined atmospherein said space to be recovered in a zone confronting the injection endsof said slow and fast jets and located at the level of said opening;injecting a fraction of the flow of the slow jet into the confinedatmosphere of the said space thereby inducing an affect on the flowrateof said slow jet; said fraction of said slow jet injected into the saidconfined atmosphere varying with the pressure within said space.
 2. Themethod of claim 1, further comprising the step of supplying the saidspace with adequate gas in order to at least compensate said recoveredfraction of the confined atmosphere.
 3. The method of claim 1, furthercomprising the step of passing products through the space for allowingprocessing of the said products in the confined atmosphere.
 4. Themethod of claim 1, wherein the said slow and fast jets are provided toconstitute a curtain of gas which is inclined towards the interior ofthe confined space with respect to the vertical axis of the saidopening.
 5. The method of claim 1, wherein the said slow and fast jetsare provided to constitute a plane curtain of gas.
 6. The method ofclaim 1, wherein the said slow and fast jets are provided to constitutea curtain of gas which describes a surface selected from the group ofthe cylindrical, truncated and polyhedral surfaces.
 7. The method ofclaim 1, wherein one of said slow jet and fast jet is supplied withthermostatted gas.
 8. The method of claim 1, wherein said slow jet andsaid fast jet are supplied with thermostatted gas.
 9. The method ofclaim 1, wherein the gas provided by said slow jet and the gas providedby said fast jet are at a common temperature.
 10. The method of claim 1,wherein said slow jet and said fast jet are air jets and wherein saidcurtain of gas constitutes a curtain of air.
 11. A device for confiningan atmosphere in a space communicating with the outside by at least oneopening by means of a curtain of gas provided at the level of saidopening, said device comprising:means for discharging a gas curtainwhich completely confines the said space, said discharge means includingfirst and second nozzle means, said second nozzle means comprising meansfor discharging a fast gas jet and said first nozzle means comprisingmeans for discharging a slow gas jet between the fast gas jet and theconfined space, said two nozzles means been disposed side by side on oneside of said opening and provided with means for supplying gas thereto,the length of said nozzle means being at least equal to the length ofsaid opening, the width of said nozzle means being determined as afunction of the velocity of fast gas jet and slow gas jet and the rangeof the curtain to be obtained; an orifice for suction of at least a partof the gas blown in from said slow and fast jets and a fraction of theconfined atmosphere, said orifice confronting said discharge means andbeing located at the level of said opening; said gas suction orificebeing located with respect to said two nozzle means and presenting ageometry such that a fraction of the flow of the slow jet is injectedinto said confined atmosphere and contributes to the induced flowrate ofsaid slow jet; said fraction varying with the pressure within saidspace.
 12. The device of claim 11, further comprising a system forsupplying the confined space with adequate gas.
 13. The device of claim11, wherein the said two nozzle means are oriented so that the generatedgas curtain is inclined towards the interior of the confined space withrespect to the vertical axis of the said opening.